Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. Typically, the orifices are arranged in one or more linear arrays in a nozzle member. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper. The paper is typically shifted each time the printhead has moved across the paper. The thermal inkjet printer is fast and quiet, as only the ink strikes the paper. These printers produce high quality printing and can be made both compact and affordable.
An inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) a metal orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is then heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper.
A series of film resistors are generally grouped together into a single microcircuit or heater chip. Typically, the heater chip is mounted on a base or substrate. The ink reservoir is generally, but not necessarily always, located below the base and the heater chip is mounted on the top of the base. Ink channel configurations can vary widely, however, one desirable configuration uses an edge feed via. In an edge feed via configuration, the ink channels extend on one or more of the edges of the heater chip. For instance, one common edge feed via configuration has two ink channels, each one delivering ink to the length-wise edges of the heater chip. The heater chips are designed to operate at a particular range of temperatures. If a heater chip overheats, a variety of problems can result, such as nozzle failure, droplet misdirection, excessive droplet splatter, etc. Typically, as the print speeds increase, more heat is generated by the heater chips. To avoid overheating, it is desirable to transfer heat away from the heater chips. Generally, the outside of a printhead include a series of cooling fins to transfer heat from the printhead to the ambient air. However, in an edge feed via configuration, the ink channels act as insulators (due in part to the relatively low thermal conductivity of ink) preventing the heat transfer from the heater chip to the cooling fins. As such, it is desirable to improve the heat transfer characteristics in a printhead.